When certain elastomers are formed as pellets or crumbs, or are shredded or are ground into particles, the crumbs, shreds or particles have a tendency to fuse together and form agglomerates that are not readily friable. The formation of agglomerates is enhanced under the temperature conditions which are usually encountered during transportation, storage or processing of elastomeric particles. Agglomerates are difficult to process in conventional equipment for processing pulverulent resins when used alone or in combination with other materials.
Non-agglomerating elastomer-containing particles have been prepared by blending an elastomer with a crystalline or semi-crystalline non-elastomeric polymer, such as polyethylene, polypropylene or copolymers of ethylene and propylene. However, such pellets are not suitable for use in many elastomer applications because high levels of the non-elastomeric polymer are required.
Mineral powders, such as silica and talc, have been added to granulated elastomers to prevent the agglomeration of the elastomeric particles. These powders can be considered to function as flow control agents which serve to separate the elastomeric particles from each other. However, in order to prevent agglomeration, it is often necessary to add the powders in such large amounts that the powdered, pulverulent elastomer, when it is being processed, no longer exhibits the properties of the unpowdered elastomer. And since the additive employed to separate the elastomer particles is itself in the form of a fine powder, it separates in time from the larger elastomeric particles to form an undesirable, non-homogeneous dusty product. In addition to interfering with processing, the dust formed can present a health or safety risk when the particles are being processed.
Elastomeric particles have been treated by dusting with various organic materials, such as hydrocarbon waxes and powdered polyolefin resins. However, the treated particles eventually come together to form agglomerates because the waxes or resins which had covered the particles tend to separate from the particles. During storage, the separated wax or resin becomes concentrated at the bottom of the container containing the elastomeric particles forming an undesirable heterogenous product.
Elastomeric particles have been coated with various coating materials by heating the particles to a temperature which is higher than the melting point of the coating material, and then contacting the heated particles with the coating material in the form of a fine powder. Since the elastomeric particles are tacky, particularly when heated, it is difficult to coat the particles evenly and obtain a uniform product using such procedure.
Another approach to the problem of preventing agglomeration has been the coating of a dispersion of elastomeric particles with a latex of a vinyl resin. Using that approach, the elastomeric particles are first dispersed in an aqueous system and then are contacted with the latex of the non-elastomeric vinyl resin. However, particles containing high levels of a non-elastomeric polymer, or whose surfaces are rigid, may not be suitable for use in many applications requiring elastomeric particles.
There is a need for non-agglomerating elastomeric particles consisting predominately of the elastomer which can be fabricated into desirable products using conventional processing equipment, and a commercially feasible method for producing such particles.
Therefore, the primary objects of the present invention are to provide a) an improved method for preventing the agglomeration of elastomeric particles during storage and transport, b) improved non-agglomerating elastomeric particles and c) a convenient method for producing those improved non-agglomerating elastomeric particles.